Porous membrane based on a polymer-filled fibrous structure

ABSTRACT

A porous membrane structure includes a fibrous host material, which defines a plurality of inter-fiber voids, and a porous guest polymer that fills at least a subset of the plurality of inter-fiber voids of the fibrous host material. The porous guest polymer facilitates selective transport of materials across the porous membrane structure and provides selective barrier properties to the porous membrane structure. The porous membrane structure may be configured as a protective barrier material for use across a range of applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. nonprovisional patent application of,and claims priority under 35 U.S.C. §119(e) to, U.S. provisional patentapplication Ser. No. 61/493,630, filed Jun. 6, 2011, which applicationis expressly incorporated by reference herein in its entirety.

APPENDIX AND INCORPORATION THEREOF BY REFERENCE

Each of the following publications and descriptions is incorporatedherein by reference in its entirety:

-   -   a) Jung, Kyung-Hye et al., “Structure-property relationships of        polymer-filled nonwoven membranes for chemical protection        applications,” made available Jun. 12, 2010 in the Journal of        Membrane Science, a copy of which is attached as Appendix A;    -   b) Jung, Kyung-Hye et al., “Chemical protection performance of        polystyrene sulfonic acid-filled polypropylene nonwoven        membranes,” made available Jul. 1, 2010 in the Journal of        Membrane Science, a copy of which is attached as Appendix B; and    -   c) Jung, Kyung-Hye et al., “Synthesis and Characterization of        Polymer-Filled Nonwoven Membranes,” submitted to Journal of        Applied Polymer Science, a copy of which is attached as Appendix        C.        The disclosure of each of the foregoing publications and        descriptions is intended to provide background and technical        information with regard to the invention described hereinbelow.

COPYRIGHT STATEMENT

All of the material in this patent document is subject to copyrightprotection under the copyright laws of the United States and othercountries. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosure,as it appears in official governmental records but, otherwise, all othercopyright rights whatsoever are reserved.

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Present Invention

The present invention relates generally to a porous membrane structure,and, in particular, to porous membrane structures prepared fromfiber-based structures and functional polymers that fill the voidswithin the fiber-based structures.

2. Background

In recent years, there has been growing interest in selective separationmembranes and selective barrier membranes for a wide range of military,industrial and consumer applications. Such applications include:supported membranes for use in a wide range of industrial andpharmaceutical processing applications; protective clothing for militaryand industrial use; personal outerwear and related garments; andbatteries and fuel cells. Interest in membrane structure has focused oncontrolling the pore structure, controlling pore size, controlling thestructure of the porous medium to improve selective separation,providing a membrane structure that is both strong and resilient underuse conditions, and providing a membrane structure that has a long uselife.

Traditional materials used to provide a selective separation membranestructure include hydrogels, polyelectrolytes (namely, ionic polymericmaterials of various types, such as anionic, cationic or betainepolymers), blocked hydrophilic non-ionic copolymers, and relatedpolymers. These materials typically swell in water and have generallypoor strength and mechanical properties. To address this issue, industryhas moved toward two types of structures.

The first such type of membrane structure involves polymer-filledmembrane technology consisting of a highly porous, robust, polymericmembrane that functions as the “host” structure and functional “guest”polymers that are used to fill the internal structure of the host film.The host film provides the necessary strength and mechanical properties,and the guest polymers, within the internal structure of the film,provide the functional micro-porous medium. Together they provide afunctional membrane that can be optimized for specific applications,including the specific selective material separations or specificselective barrier properties. Examples of technologies that haveattempted to address specific needs utilizing this approach are setforth in the following patents and published patent applications:

-   -   U.S. Patent Application Publication No. to Isomura et al. US        2010/0279204 A1 which is directed to the preparation of a        separation membrane for fuel cells that include a porous film,        where the pores are filled with a polymeric ion exchange        composition that is generated by polymerizing selected monomers        within the pores and then functionalizing the polymers;    -   U.S. Pat. No. 7,868,051 to Fukuta et al., which is directed to        the preparation of a membrane for fuel cells by filling the        voids of a porous membrane with a cross-linking ion exchange        resin;    -   U.S. Pat. No. 7,824,820 to Yamaguchi et al., which is directed        to the preparation of an electrolyte membrane based on filling        the pores of a porous film with a polymer that is capable of        conducting protons;    -   U.S. Pat. No. 7,749,629 to Hommura et al., which is directed to        the preparation of an electrolyte membrane based on filling the        pores of a porous melt-moldable fluoro-chemical resin film with        an ion exchange polymer; and    -   U.S. Pat. No. 7,674,349 to Hiraoka et al., which is directed to        a method for the continuous production of a functional membrane        film based on filling the pores of a porous resin sheet with        polymeric precursors that are then polymerized to generate the        membrane film.

While polymer-filled, highly porous membranes have much higher strengthand mechanical properties as compared against simple unsupported polymermembranes, a significant deficiency in current filled-membranetechnologies involves long-term durability, which remains poor. Inpolymer-filled, highly porous membranes, the host membrane experienceslarge stresses while suppressing the swelling of the functional guestpolymer. As a result, the system often loses its integrity during use,especially in applications where the membranes face repeated hydrationand dehydration (i.e., repeated swelling and contraction). Furthermore,the system's ability to function is dictated completely by the volumecapacity of the filled pores that provide a complete path through themembrane structure. The system's ability to separate effectively is afunction of the guest polymer's ability to selectively transportmaterials across the filled voids within the membrane structure. Thevolume percent of “completed paths” through the structure is oftenlimited.

The second type of membrane structure involves supported membranes,which include technologies where the membrane film itself is supportedthrough the use of an external structure. Such structures include a widearray of external support structures ranging from porous metal plates tovarious types of fabrics. In these membrane structures, the functionalmembrane provides the desired performance while the external structuresprovide support and protection for the membrane. Examples oftechnologies that have attempted to address the development of specificmembranes of this type are set forth in the following patents andpublished patent applications:

-   -   U.S. Patent Application Publication No. US 2010/0075101 A1 to        Tang, which is directed to the preparation of supported        separation membranes for gas and liquid materials based on a        membrane applied directly to a tricot fabric;    -   U.S. Pat. No. 7,569,616 to Kotera et al., which is directed to        the generation of electrolytic ion exchange membranes for fuel        cells based on the use of a reinforced inner layer of a        fluoro-polymer-based non-woven fabric structure;    -   U.S. Pat. No. 6,919,026 to Hama et al., which is directed to the        preparation of specific nonwoven materials to be used as        supports for membrane materials;    -   U.S. Pat. No. 6,645,420 to Beck, which is directed to the        preparation of a membrane structure based on the incorporation        of a unitary, formed carrier fabric to provide support for the        formed membrane; and    -   U.S. Pat. No. 6,484,887 to Fukutomi et al., which is directed to        the preparation of ion-selective membranes that are supported by        woven fabric shaped backings.

While external supports in current supported membrane technologiesprovide improved stability for the functional membrane structure, suchsupports, at the same time, tend to restrict flow through the membrane.There are also serious issues with bonding of the membrane to thesupport structure and maintaining the stability of the bonded structurethrough the swelling and contractions associated with functionalmembrane structures. While these types of structures tend to provide forhigher transport of materials through the membrane, when one considersinterference or diffusion requirements for materials through theexternal support structures, the net effect is a low-performing andshort-lived membrane.

Accordingly, there remains a need for improved, selective separation andselective barrier membranes that provide high strength and long-termstructural stability, a high level of permeability, and a high level ofselectivity functionality. This and other needs are addressed by one ormore aspects of the present invention.

SUMMARY OF THE PRESENT INVENTION

The present invention comprises a porous membrane structure comprising afibrous host material and a porous guest polymer.

Broadly defined, the present invention according to a first aspectincludes a porous membrane structure that includes a fibrous hostmaterial and a porous guest polymer. The fibrous host material providesstructure to a membrane and defines a plurality of inter-fiber voids.The porous guest polymer fills at least a portion of the inter-fibervoids of the fibrous host material.

In features of this aspect, the fibrous host material may include awoven material; the fibrous host material may include a nonwovenmaterial; and the fibrous host material may include a knit fabricmaterial.

In further features of this aspect, the porous guest polymer mayfacilitate selective transport of materials across the membrane; and theporous guest polymer may provide selective barrier properties across themembrane.

In still further features of this aspect, the fibrous host material maycomprise approximately 3% to approximately 40% of the total weight; thefibrous host material may comprise approximately 5% to approximately 30%of the total weight; the fibrous host material may compriseapproximately 10% to approximately 25% of the total weight; the porousguest polymer may comprise approximately 60% to approximately 97% of thetotal weight; the porous guest polymer may comprise approximately 70% toapproximately 95% of the total weight, and the porous guest polymer maycomprise approximately 75% to approximately 90% of the total weight.

In still further features of this aspect, the porous guest polymer mayinclude a polymer based on free-radical polymerizations of vinyl,acrylate, or methacrylate intermediates that are chain-extended orcross-linked with di- or poly-functional intermediates; the porous guestpolymer may include a polymer based on pre-polymers and reactiveintermediates; and the porous guest polymer may include a polymer basedon pre-formed polymers that can be applied from solvents or water.

In still another feature of this aspect, the fibrous host material maybe a flexible material.

Broadly defined, the present invention according to a second aspectincludes a membrane structure substantially as shown and described.

Broadly defined, the present invention according to a third aspectincludes a membrane that includes a fibrous host material and a porousguest polymer. The porous guest polymer is configured to provideselective transport of materials across the membrane or selectivebarrier properties across the membrane.

Broadly defined, the present invention according to a fourth aspectincludes a membrane that includes a fibrous host material and a porousguest polymer. The fibrous host material comprises approximately 3% toapproximately 40% of the total weight, and the porous guest polymercomprises approximately 60% to approximately 97% of the total weight.

In a feature of this aspect, the fibrous host material may compriseapproximately 5% to approximately 30% of the total weight, and theporous guest polymer may comprise approximately 70% to approximately 95%of the total weight. In another feature of this aspect, the fibrous hostmaterial may comprise approximately 10% to approximately 25% of thetotal weight, and the porous guest polymer may comprise approximately75% to approximately 90% of the total weight.

Broadly defined, the present invention according to a fifth aspectincludes a protective barrier material that includes a porous membranestructure. The porous membrane structure includes a fibrous hostmaterial, which defines a plurality of inter-fiber voids, and a porousguest polymer that fills at least a subset of the plurality ofinter-fiber voids of the fibrous host material. The porous guest polymerfacilitates selective transport of materials across the porous membranestructure and provides selective barrier properties to the porousmembrane structure.

In features of this aspect, the fibrous host material may include anonwoven material; and the fibrous host material may be a flexiblematerial.

In further features of this aspect, the fibrous host material maycomprise approximately 3% to approximately 40% of the total weight ofthe porous membrane structure; the fibrous host material may compriseapproximately 5% to approximately 30% of the total weight of the porousmembrane structure; and the fibrous host material may compriseapproximately 10% to approximately 25% of the total weight of the porousmembrane structure.

In still further features of this aspect, the porous guest polymer maycomprise approximately 60% to approximately 97% of the total weight ofthe porous membrane structure; the porous guest polymer may compriseapproximately 70% to approximately 95% of the total weight of the porousmembrane structure; and the porous guest polymer may compriseapproximately 75% to approximately 90% of the total weight of the porousmembrane structure.

In still further features of this aspect, the porous guest polymer mayfacilitate transfer of water vapor across the porous membrane structureand may provide barrier properties against a toxic chemical; the porousguest polymer may include a PAMPS polymer; the porous guest polymer mayinclude a PSS polymer; and the porous guest polymer may include a PMApolymer.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, embodiments, and advantages of the present inventionwill become apparent from the following detailed description withreference to the drawings, wherein:

FIG. 1 is a graph illustrating tensile properties of porous membranesbased on polymer-filled fibrous structures;

FIG. 2 is a graph illustrating vapor permeability of PAMPS membraneswith respect to moisture transport and transport of chemical warfareagent simulants (represented by the transport of dimethyl methylphosphate (DMMP)).

FIG. 3A is a graph illustrating water vapor permeability of membranesbased on polymer-filled fibrous structures; and

FIG. 3B is a graph illustrating DMMP vapor permeability of membranesbased on polymer-filled fibrous structures.

DETAILED DESCRIPTION

As a preliminary matter, it will readily be understood by one havingordinary skill in the relevant art (“Ordinary Artisan”) that the presentinvention has broad utility and application. Furthermore, any embodimentdiscussed and identified as being “preferred” is considered to be partof a best mode contemplated for carrying out the present invention.Other embodiments also may be discussed for additional illustrativepurposes in providing a full and enabling disclosure of the presentinvention. Moreover, many embodiments, such as adaptations, variations,modifications, and equivalent arrangements, will be implicitly disclosedby the embodiments described herein and fall within the scope of thepresent invention.

Accordingly, while the present invention is described herein in detailin relation to one or more embodiments, it is to be understood that thisdisclosure is illustrative and exemplary of the present invention, andis made merely for the purposes of providing a full and enablingdisclosure of the present invention. The detailed disclosure herein ofone or more embodiments is not intended, nor is to be construed, tolimit the scope of patent protection afforded the present invention,which scope is to be defined by the claims and the equivalents thereof.It is not intended that the scope of patent protection afforded thepresent invention be defined by reading into any claim a limitationfound herein that does not explicitly appear in the claim itself.

Thus, for example, any sequence(s) and/or temporal order of steps ofvarious processes or methods that are described herein are illustrativeand not restrictive. Accordingly, it should be understood that, althoughsteps of various processes or methods may be shown and described asbeing in a sequence or temporal order, the steps of any such processesor methods are not limited to being carried out in any particularsequence or order, absent an indication otherwise. Indeed, the steps insuch processes or methods generally may be carried out in variousdifferent sequences and orders while still falling within the scope ofthe present invention. Accordingly, it is intended that the scope ofpatent protection afforded the present invention is to be defined by theappended claims rather than the description set forth herein.

Additionally, it is important to note that each term used herein refersto that which the Ordinary Artisan would understand such term to meanbased on the contextual use of such term herein. To the extent that themeaning of a term used herein—as understood by the Ordinary Artisanbased on the contextual use of such term—differs in any way from anyparticular dictionary definition of such term, it is intended that themeaning of the term as understood by the Ordinary Artisan shouldprevail.

Furthermore, it is important to note that, as used herein, “a” and “an”each generally denotes “at least one,” but does not exclude a pluralityunless the contextual use dictates otherwise. Thus, reference to “apicnic basket having an apple” describes “a picnic basket having atleast one apple” as well as “a picnic basket having apples.” Incontrast, reference to “a picnic basket having a single apple” describes“a picnic basket having only one apple.”

When used herein to join a list of items, “or” denotes “at least one ofthe items,” but does not exclude a plurality of items of the list. Thus,reference to “a picnic basket having cheese or crackers” describes “apicnic basket having cheese without crackers,” “a picnic basket havingcrackers without cheese,” and “a picnic basket having both cheese andcrackers.” Finally, when used herein to join a list of items, “and”denotes “all of the items of the list.” Thus, reference to “a picnicbasket having cheese and crackers” describes “a picnic basket havingcheese, wherein the picnic basket further has crackers,” as well asdescribes “a picnic basket having crackers, wherein the picnic basketfurther has cheese.”

Referring now to the drawings, the preferred embodiments of the presentinvention are next described. The following description of one or morepreferred embodiment(s) is merely exemplary in nature and is in no wayintended to limit the invention, its application, or uses.

In accordance with one or more embodiments of the present invention,structured membranes can be generated by using a fiber-based “host”matrix, where the voids within the fiber-based host matrix are filledwith a functional “guest” polymer. These fiber-based, filled membranestructures address many of the deficiencies that are prevalent in thecurrent membrane technologies. Membrane structures in accordance withthe present invention have high long-term structural stability, a highconcentration of effective paths through the functional guest polymer(i.e., higher level of transport through the membrane), and aninteractive mechanism between the structural component of the membraneand the functional guest polymer that enhances the ability of thefunctional guest polymer to provide effective separation (i.e.,tortuosity).

In these structured membranes, the fabric structure provides membranestrength and mechanical properties while supporting membrane integrityduring its use life. Further, these membrane structures provide a novel,flexible matrix for the functional guest polymers. Still further, thesemembrane structures support a high level of transport by providing ahigh concentration of effective paths through the functional guestpolymer and by also providing a level of tortuosity, within thefiber-based structure, which has been shown to enhance the separationefficiency of the functional guest polymer. Membranes in accordance withthe present invention thus may have significant advantages over currentmembrane technology in terms of being able to supply desirableproperties such as high levels of material transport, high performancein selective separations, structural strength, mechanical stability, anda range of tunable properties including flexibility, chemicalresistance, and penetration resistance.

Fiber-based structures suitable for this application include a widerange of woven, non-woven and knit fabric structures. The wide range offiber-based structures that can be used in this application provides fora wide, diverse range of membrane structures, which results in a widerange of performance properties that can be generated. In addition, bycontrolling the structure of the fiber structure and the diameter of thefibers used in the structure, it is possible to generate controlledlevels of tortuosity within the final membrane structure, which cansignificantly modify the selective character of the separation that isgenerated using the membrane. The flexibility of the fiber-basedstructures can be matched to that of the guest polymer that is used tofill the voids within the structure and, in this way, a product can bedesigned that has sufficient internal flexibility to withstand repeatedswelling and contractions associated with the guest functional polymer,thereby providing separation membranes that have long-term mechanicaland material stability.

Advantages associated with using a fiber-based matrix as the hostframework for a polymer filled membrane include:

-   -   the fiber-based structure can provide strength together with the        flexibility needed to support long term mechanical and        functional stability within the membrane structure;    -   the fiber-based structure has a high internal capacity for the        guest functional polymer, thereby generating high levels of        transport across the membrane structure;    -   the host framework can be constructed from a wide range of        different polymers that can be selected for desirable secondary        properties such as chemical resistance, low ion interaction, or        structural flexibility;    -   the host structure can be designed to improve the performance of        the guest functional polymer by providing tortuosity within the        structural matrix, which can be used to generate improved        separation properties;    -   the thickness and the ratio of fiber-based host matrix to        functional guest polymer within the membrane can be precisely        controlled;    -   the functional and mechanical properties of the fiber-based        structure can be tuned by controlling the volume fraction of the        guest functional polymer occluded in the pores of the host        framework; and    -   the nature of the system provides a high level of flexibility in        the types of functional guest polymers that can be considered,        thereby generating the technology for supporting a full range of        membrane applications.

The present invention includes a fibrous structure (the “host”structure) that has been filled with a hydrophilic polymer composition(the “guest” polymer). The composition of the guest polymer can then bematched to the properties of the host structure and to the requirementsof the application that is being envisioned for the membrane. Together,the host structure and guest polymer can provide a high-performancemembrane product.

The fibrous host structure can be constructed from a wide range offibrous materials depending on the specifics of the application. Suchfibrous material may include, but are not limited to: polyolefinpolymers, such as polyethylene and polypropylene; condensation polymers,such as the wide range of polyester and nylon polymers that arecommercially available; high-performance polymers such as polyphenylenesulfide, KEVLAR or NOMEX; solution or solvent spun polymers, such asacetates, acrylics and rayon; natural fibers, such as cotton, wool andsilk; highly polar polymers, such as polyvinyl alcohol and modifiedpolyvinyl alcohol polymers; and other specialty polymers, such aselastaines, flame-retardant polymers, or fibers based on polymerstructures specifically designed for a membrane application. The presentinvention is not limited to the nature of the polymer used in the fiber,the selection of which may be significant to particular applications.

Fibrous host structures can also be selected from a wide range of fabricstructures that are available. Such fabric structures may include, butare not limited to: woven materials of various structures, includingvarious weaves and modified woven structures, woven materials preparedusing fine denier and micro-denier fibers, and 3-D woven structures;knit structures of various types; and nonwoven materials, includingcarded and point bonded fabrics, carded and powder bonded or fiberbonded fabrics, spunbond, SMS or related bonded fabrics, spun lace orneedled fabrics, air lay or wet lay fabrics, and the like. The presentinvention is not limited to the nature of the host fabric structure thatis used to support and provide tortuosity within the membrane, theselection of which may be significant to particular membraneapplications.

The guest polymer composition can also be selected from a wide range ofavailable polymeric structures. Such polymers may be applied as monomersand then reacted within the fibrous matrix to generate the guestpolymer. Such polymers may also be applied as pre-polymers and thenchain-extended and/or cross-linked within the fibrous matrix to generatethe guest polymer. Additionally, specific polymers may be applied as asolvent solution that is deposited within the fibrous matrix as thesolvent is removed. There are a wide range of guest polymeric materialsthat can be utilized to generate functional membrane materials that fillthe voids within the fiber-based structure.

For instance, guest polymeric materials may include hydrogels orpolyelectrolytes. Additionally, guest polymeric materials may includepolymers that are based on free-radical polymerizations of vinyl,acrylate, or methacrylate intermediates that are cross-linked with di-or poly-functional intermediates. Such materials are applied as monomersand then free-radical polymerized within the matrix. The inclusion ofdi- or-poly-functional materials in the formulation, appropriate to thereactive system, function to cross-link and stabilize the membrane finalstructure.

Further, guest polymeric materials may include functional pre-polymersthat are prepared and applied to the fiber-based structure along withchain extension and/or cross-linking materials based on reactive,poly-functional intermediates. For hydroxyl or amine functionalpre-polymers, suitable reactive cross-linking materials can includeepoxy, blocked urethane, or similar functional intermediates.Conversely, the pre-polymer may be reactive functionalized (such asepoxy, blocked urethane or the like) and the chainextending/cross-linking material would be a di- or poly-functionalpre-material or polymer having functional groups suitable to extendingand cross-linking the polymeric material. In either case, polymerizationwould be completed by a heating process to generate the stabilizedmembrane.

Still further, guest polymeric materials may include polymers that areprepared and applied to the fiber-based structure as solvent- orwater-based solutions and that then generate a stable membrane structureonce the solvent/water is removed.

For functional activity, the polymers generated are typically polarstructures with a high concentration of ionic or polar non-ionicstructures. By cross-linking the structures, one obtains a stable,water-swellable membrane structure that is then the basis for selectivemovement of materials across the membrane. The present invention is notlimited to the nature of the guest polymer that provides the functionalmedium within the membrane, the selection of which may be significant toparticular membrane applications.

In accordance with the present invention, advantages can be obtainedfrom the generation of membrane structures that are based on a hostfibrous structure and a guest polymer that fills the voids within thehost fibrous structure. Utilizing this technology leads to significantand previously unexpected advantages as compared with existing membranetechnologies. Such advantages include, but are not limited to: membranesthat have high strength and avoid many of the issues that shorten theworking life or reduce the efficiency of other membrane structures;membranes that have very high material transfer rates that are notlimited by the structure of external secondary supporting materials orby the volume of porous channels within a host structure; and membranesthat have enhanced separation characteristics based on the developmentof tortuosity within the host-guest structure, which providesimprovements in the separation of materials based on polarity, molecularsize, molecular weight, or combinations of these properties. Suchmembrane structures are highly functional and are understood torepresent a significant improvement in the development of new membranestructures.

Membranes in accordance with one or more aspects of the presentinvention may be those where the structure is based on a host fibrousstructure that makes up approximately 3% to 40% of the weight of thefinal membrane and a guest porous polymer that fills in the inter-fibervoids within the host structure and makes up approximately 60% to 97% ofthe weight of the final membrane. Additionally, membranes in accordancewith one or more aspects of the present invention may be those withstructures based on a host fibrous structure that is then filled with afunctional guest polymer to generate the membrane structure.

The present invention according to a preferred embodiment includes amembrane composed of a fiber-based structure as a host fibrousstructure, where the voids within that structure are filled with aporous polymer material as a guest polymer.

In preferred aspects, the host fiber-based structure may be selectedfrom the materials summarized below.

-   -   Materials may include woven fabrics based on various polymer        types, fiber diameters and cross-sections, weaves, and        constructions.    -   Materials may include nonwoven fabrics based on the range of        nonwovens processes including spun-bonded, melt-blown, card and        needle punched, card and bond with thermal or polymer bonding        agents, card and spun lace, air lay, wet lay, along with various        composite nonwoven processes and the like.

In preferred aspects, the porous guest polymer may be selected from theclasses summarized below.

-   -   Polymers may include polymers based on free-radical        polymerizations of vinyl, acrylate, or methacrylate        intermediates that are chain-extended and/or cross-linked with        appropriate di- or poly-functional intermediates.    -   Polymers may include polymers based on pre-polymers and reactive        intermediates. In these formulations, the reactive intermediates        of various types serve to create a stable high molecular weight        polymer material through chain-extension and cross-linking        mechanisms. Desirable pre-polymers are low molecular weight        materials with available functionality in the form of amine or        hydroxyl groups, and desirable reactive intermediates are        monomers of low molecular weight polymers with reactive        functionality (such as blocked urethanes, epoxy, or a similar        reactive structure).    -   Polymers may include pre-formed polymers that can be applied        from solvents or water to form a stable membrane structure as        the solvent/water is removed.        The first two classes of materials may be combined with the host        structure in such a way that the polymeric intermediates that        will be used to generate the guest polymer penetrate the host        fiber-based structure and fill the voids of that structure and        are then polymerized by chain-extension and/or cross-linking to        generate the stable porous guest polymer. The latter class is        applied and the functional polymer is deposited as the solvent        is removed.

In a preferred embodiment of such porous membrane structures, thefibrous host structure makes up approximately 5% to 30% of the weight ofthe final membrane structure, and the porous guest polymer makes upapproximately 70% to 95% of the weight of the final membrane structure.In another preferred embodiment, the fibrous host structure makes upapproximately 10% to 25% of the weight of the final membrane structure,and the porous guest polymer makes up approximately 75% to 90% of theweight of the final membrane structure.

EXAMPLES

Outlined below are examples of the preparation of membranes inaccordance with the present invention. The following examples areprovided for illustrative purposes and do not limit or otherwise impairthe scope of the present invention.

Example 1 Polystyrene Sulfonic Acid (PSS) Filled Fabric Based Membrane

Polymer materials used in the preparation of the PSS-based membrane areas follows:

-   -   Sodium 4-vinylbenzenesulfonate (NaVBS)    -   2,2′-Azobis(2-methyl proprionitrile) (AIBN) (free radical        initiator)    -   Divinyl benzene (DVB) (cross-linking agent)    -   Dimethyl sulfoxide (DMSO)

The PSS membrane was synthesized by free-radical polymerization from themonomer blend of NaVBS and DVB, followed by post-polymerizationion-exchange of the Na⁺ with H⁺ in a 30 gram nonwoven fabric(polypropylene card and bond).

Preparative steps are summarized as follows. 1.0 mole/1 NaVBS, 0.1mole/1 AIBN & 0.1 mole/1 DVB were dissolved in DMSO. Polypropylenenonwovens were soaked in the DMSO solution mixture and placed betweenTeflon plates. The plates were heated at 60° C. under vacuum for 4hours. The resulting PSS-filled membranes were washed in distilled waterand vacuum-dried for 24 hours. To obtain compact, thinner membranes, thedried PSS-filled nonwoven membranes were compressed using hot pressureunder 17 MPa at 95° C. for 1 minute. The membrane was then subjected toion-exchange to provide the acid form of the membrane.

The chemical structure of the polymer used to generate the PSS-basedmembrane is as follows:

Example 2 Poly(2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) (PAMPS)Based Unsupported Membrane

Materials used in the preparation of the PAMPS-based membrane are asfollows:

-   -   2-Acrylomido-2-methyl-1-propanesulfonic acid (AMPS)    -   2,2′-Azobis(2-methyl proprionitrile) (AIBN)    -   Ethylene glycol dimethacrylate (EGDM)    -   Dimethyl sulfoxide (DMSO)

The PAMPS-based membrane was synthesized by free-radical polymerizationof AMPS and EGDM to generate an unsupported film.

Preparative steps are summarized as follows. 1.0 mole/1 AMPS, 0.10mole/1 AIBN and 0.10 mole/1 of EGDM were dissolved in DMSO. The solutionmixture was placed, with a spacer, between two TEFLON plates. The plateswere heated at 60° C. under vacuum for 4 hours. The resultingunsupported PAMPS membranes were washed in distilled water andvacuum-dried for 24 hours. To obtain compact, thinner membranes thedried unsupported PAMPS membranes were compressed using hot pressureunder 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PAMPS-basedmembrane is as follows:

Example 3 Poly(2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) (PAMPS)Filled Fabric Based Membrane

Materials used in the preparation of the PAMPS-based membrane are asfollows:

-   -   2-Acrylomido-2-methyl-1-propanesulfonic acid (AMPS)    -   2,2′-Azobis(2-methyl proprionitrile) (AIBN)    -   Ethylene glycol dimethacrylate (EGDM)    -   Dimethyl sulfoxide (DMSO)

The PAMPS-based membrane was synthesized by free-radical polymerizationof AMPS and EGDM in a 30 gram nonwoven fabric (polypropylene card andbond).

Preparative steps are summarized as follows. 1.0 mole/1 AMPS, 0.10mole/1 AIBN and 0.10 mole/1 of EGDM were dissolved in DMSO.Polypropylene nonwovens were soaked in the solution mixture and placedbetween 2 Teflon plates. The plates were heated at 60° C. under vacuumfor 4 hours. The resulting PAMPS-filled membranes were washed indistilled water and vacuum-dried for 24 hours. To obtain compact,thinner membranes the dried PAMPS-filled nonwoven membranes werecompressed using hot pressure under 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PAMPS-basedmembrane is as follows:

Example 4 Polymethyl Acrylic Acid (PMA) Based Membrane

Materials used in the preparation of the PMA-based membrane are asfollows:

-   -   Methacrylic acid (MA)    -   Potassium peroxodisulfate (PPS)    -   Ethylene glycol dimethacrylate (EGDM)    -   Distilled water

The PMA membrane was synthesized by free-radical polymerization from themonomer MA and EGDM in a 30 gram nonwoven fabric (polypropylene card andbond).

Preparative steps are summarized as follows. 1.0 mole/1 MA, 0.10 mole/1PSS and 0.10 mole/1 of EGDM were dissolved in distilled water.Polypropylene nonwovens were soaked in the solution mixture and placedbetween 2 Teflon plates. The plates were heated at 60° C. under vacuumfor 4 hours. The resulting PMA-filled membranes were washed in distilledwater and vacuum-dried for 24 hours. To obtain compact, thinnermembranes the dried PMA-filled nonwoven membranes were compressed usinghot pressure under 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PMA-basedmembrane is as follows:

FIG. 1 is a graph illustrating tensile properties of porous membranesbased on polymer-filled fibrous structures. As shown in FIG. 1, theunsupported membranes are very weak, and the filled membranes aregenerally stronger then the non-woven fabric itself.

Membranes were evaluated as potential barrier fabrics. Barrier fabricsare designed to provide high moisture transport along with low transportof chemical warfare agent simulants (represented in the following databy the transport of dimethyl methyl phosphate (DMMP), a simulant for thenerve gas agent Sarin). FIG. 2 is a graph illustrating vaporpermeability of PAMPS membranes with respect to moisture transport andtransport of chemical warfare agent simulant DMMP. The membranesprovided a high level of moisture transport with relatively low valuesfor DMMP transport. As further shown in FIG. 2, while the unsupportedmembrane did provide high moisture transport and relatively low DMMPtransport, the filled membranes yielded lower values in bothmeasurements and the reduction in DMMP transport is clearly higher thanthat of water. This is believed to be due to the tortuosity effectintroduced by the fabric structure, which is understood to be asignificant enhancement of membrane performance.

FIG. 3A is a graph illustrating water vapor permeability of membranesbased on polymer-filled fibrous structures, and FIG. 3B is a graphillustrating DMMP vapor permeability of membranes based onpolymer-filled fibrous structures. The PSS, PAMPS and PMA basedmembranes were also evaluated as protective membranes. As shown in FIGS.3A and 3B, all three polymer classes are relatively consistent inperformance, showing that the membranes generated according to theinvention yielded both high moisture transport and low transport of thenerve gas simulant DMMP (thereby indicating a high ability to transfermoister while functioning as a barrier to nerve gas). The data alsoillustrates that the filled fabric membranes provide significantlyimproved barrier properties against DMMP with minimal reduction inmoisture transport results. As noted above, these results are believedto be the effect of tortuosity introduced by the fabric structure.

As shown in the data, membranes in accordance with the present inventionhave significantly enhanced separation properties (i.e., selectiveblocking of materials) while maintaining optimal performance withrespect to water vapor permeability. In particular, water vapor transfercapabilities and performance of membranes in accordance with the presentinvention is at or near 100% of such capabilities for known membranestructures.

Membranes in accordance with the present invention may be tuned for awide range of particular applications. These membrane structures mayhave utility as barrier membranes for military and industrial chemicalprotection applications, breathable barrier fabrics for a range ofpersonal clothing applications, or as separation membranes for a rangeof different applications, such as water treatment, mineral extraction,bio-separations, filters, sensors, biocatalysts, supercapacitors, datastorage, energy generation, micro-electronics and semiconductors, drugdelivery, pharmaceutical purification, artificial blood vessels, tissuegrowth, environmental processes, ultra-filtration, materials synthesis,batteries and fuel cells, as well as various other applications.

Based on the foregoing information, it will be readily understood bythose persons skilled in the art that the present invention issusceptible of broad utility and application. Many embodiments andadaptations of the present invention other than those specificallydescribed herein, as well as many variations, modifications, andequivalent arrangements, will be apparent from or reasonably suggestedby the present invention and the foregoing descriptions thereof, withoutdeparting from the substance or scope of the present invention.

Accordingly, while the present invention has been described herein indetail in relation to one or more preferred embodiments, it is to beunderstood that this disclosure is only illustrative and exemplary ofthe present invention and is made merely for the purpose of providing afull and enabling disclosure of the invention. The foregoing disclosureis not intended to be construed to limit the present invention orotherwise exclude any such other embodiments, adaptations, variations,modifications or equivalent arrangements; the present invention beinglimited only by the claims appended hereto and the equivalents thereof.

What is claimed is:
 1. A porous membrane structure comprising: (a) afibrous host material for providing structure to a membrane, the fibroushost material defining a plurality of inter-fiber voids; and (b) aporous guest polymer that fills at least a subset of the plurality ofinter-fiber voids of the fibrous host material.
 2. The porous membranestructure of claim 1, wherein the fibrous host material includes anonwoven material.
 3. The porous membrane structure of claim 1, whereinthe porous guest polymer facilitates selective transport of materialsacross the membrane.
 4. The porous membrane structure of claim 1,wherein the porous guest polymer provides selective barrier propertiesto the membrane.
 5. The porous membrane structure of claim 1, whereinthe fibrous host material comprises approximately 3% to approximately40% of the total weight.
 6. The porous membrane structure of claim 5,wherein the fibrous host material comprises approximately 10% toapproximately 25% of the total weight.
 7. The porous membrane structureof claim 1, wherein the porous guest polymer comprises approximately 60%to approximately 97% of the total weight.
 8. The porous membranestructure of claim 7, wherein the porous guest polymer comprisesapproximately 75% to approximately 90% of the total weight.
 9. Theporous membrane structure of claim 1, wherein the fibrous host materialis a flexible material.
 10. A protective barrier material comprising:(a) a porous membrane structure, the porous membrane structure includinga fibrous host material, which defines a plurality of inter-fiber voids,and a porous guest polymer that fills at least a subset of the pluralityof inter-fiber voids of the fibrous host material; (b) wherein theporous guest polymer facilitates selective transport of materials acrossthe porous membrane structure and provides selective barrier propertiesto the porous membrane structure.
 11. The protective barrier material ofclaim 10, wherein the fibrous host material includes a nonwovenmaterial.
 12. The protective barrier material of claim 10, wherein thefibrous host material is a flexible material.
 13. The protective barriermaterial of claim 10, wherein the fibrous host material comprisesapproximately 3% to approximately 40% of the total weight of the porousmembrane structure.
 14. The protective barrier material of claim 13,wherein the fibrous host material comprises approximately 10% toapproximately 25% of the total weight of the porous membrane structure.15. The protective barrier material of claim 10, wherein the porousguest polymer comprises approximately 60% to approximately 97% of thetotal weight of the porous membrane structure.
 16. The protectivebarrier material of claim 15, wherein the porous guest polymer comprisesapproximately 75% to approximately 90% of the total weight of the porousmembrane structure.
 17. The protective barrier material of claim 10,wherein the porous guest polymer facilitates transfer of water vaporacross the porous membrane structure and provides barrier propertiesagainst a toxic chemical.
 18. The protective barrier material of claim17, wherein the porous guest polymer includes a PAMPS polymer.
 19. Theprotective barrier material of claim 17, wherein the porous guestpolymer includes a PSS polymer.
 20. The protective barrier material ofclaim 17, wherein the porous guest polymer includes a PMA polymer.